This invention relates to synthetic turfs for athletic fields and, more particularly, to a synthetic turf filled with particulate material so as to give the field stability and resiliency.
A natural grass turf covering has traditionally been cultivated on playing surfaces for athletic games or events. In addition to looking good, natural grass turf provides inherent resiliency and cushioning, thereby minimizing the risk of injury due to an athlete""s impact with the turf. Such natural grass turf coverings have traditionally been used to cover American football or soccer fields. Many athletes participating in these high impact sports desire a surface with a high degree of resiliency such as is provided by a natural grass turf covering.
However, maintenance of natural grass turf on athletic playing areas can be expensive and time consuming. Natural grass does not grow well within shaded areas like those within indoor or partially enclosed stadiums. In addition, some xe2x80x9cheavy trafficxe2x80x9d locations on the playing field are susceptible to wearing out or deteriorating due to continuous or excessive wear. These worn areas may become muddy and slippery after the natural grass dies, increasing the likelihood of injury.
Therefore, various types of synthetic turf have been developed and installed on athletic playing surfaces, particularly surfaces located within indoor stadiums. Generally, these various synthetic turf surfaces reduce the expense of maintaining athletic playing surfaces and increase the durability of the turf surface. Synthetic turf generally comprises a flexible backing and a plurality of grass-like pile filaments or fibers extending upwardly from the backing. The flexible backing is typically laid on a foundation or compacted substrate, such as crushed stone or stabilized base material.
Most earlier forms of synthetic turf relied solely on the backing and the pile filaments or fibers as the playing surface. ASTROTURF synthetic turf is an example of this type of artificial turf.
In order to give the synthetic turf a desired degree of resiliency and stability, various formulations of granular fill material may be placed between or among the upstanding pile filaments of the synthetic turf. This granular fill material extends upwardly from the upper surface of the backing to a height below the tops of the pile filaments, thereby leaving upper portions of the pile filaments exposed for aesthetic purposes, among others. The granular fill material helps maintain in a substantially upright condition the filaments of the synthetic turf. This granular fill material has been sand, crushed slag particles, resilient foam, crumb rubber particles, sand or various combinations thereof.
U.S. Pat. No. 3,995,079 discloses a filled synthetic turf for golf greens, the granular fill material being granulated coal slag, crushed flint or crushed granite. The difficulty with the use of these particles as fill material is that they are very abrasive. This inherent abrasiveness increases the probability of scrapes or abrasions to persons falling upon the filled synthetic turf.
U.S. Pat. No. 4,044,179 discloses a filled synthetic turf for athletic playing surfaces, wherein the granular fill material is sand with a small amount of moisture retaining material. The difficulty with the use of sand as the fill is that sand compacts over time and use, resulting in a filled synthetic turf which is harder than desired. Because such playing surfaces are commonly used for high impact sports, the harder the field, the greater the likelihood of injury for the players using the field. Another difficulty with sand as the fill material is that sand retains water or moisture, thereby increasing the susceptibility of the filled synthetic turf to mold or mildew.
U.S. Pat. No. 4,337,283 discloses a filled synthetic turf for athletic playing surfaces, the granular fill material being a uniformly mixed combination of sand particles and resilient particles. One inherent difficulty with the use of such a mixture is that the resilient particles of the mixture tend to migrate to the top of the fill layer over time and repeated use with the sand tending to settle below the resilient particles. The sand that settles to the bottom of the fill layer tends to compact over time and use. This ultimately results in a layered synthetic turf which is harder and more abrasive than desired. A further disadvantage of such a uniformly mixed in fill is that some abrasive sand particles remain on the top surface of the synthetic turf. Players who come into contact with the sand particles experience skin abrasions.
U.S. Pat. No. 5,958,527 discloses a filled synthetic turf for athletic playing surfaces, the granular fill material comprising separate layers of sand particles and resilient particles. Difficulties with such a layered mixture are over time and repeated use, the sand at the bottom of the mixture tends to compact, causing the field to harden and inhibiting the vertical drainage of water off the field through the backing fo the filled synthetic turf.
Because filled synthetic turfs are subject to large temperature fluctuations, resulting in contraction and expansion of the turf backing, a fill comprising at least one layer of sand stabilizes the backing of the synthetic turf and provides weight to minimize lateral movement of the backing. However, over time and use, the sand particles are churned up or migrate toward the top of the field. The resilient particles in known filled synthetic turfs may migrate laterally due to the dynamic nature of the fill material. Athlete""s cleats and other wear churns or mixes the fill material, resulting in a non-uniform playing surface with areas of exposed sand. Abrasive sand particles migrate to or find their way to the surface of the synthetic turf between the pile filaments. Whenever athletes fall or contact the turf, they are subject to cuts or abrasions due to the sand. The sand particles located at the surface of the fill material also are abrasive to the pile filaments of the synthetic turf, thereby degrading and/or fibrillating the tops of the pile filaments over time.
In addition, over time the sand compacts and becomes harder, an undesirable quality for a synthetic playing surface. Then, the resilient effect of the rubber particles is only temporary.
Therefore, it is an object of this invention to hold down the backing of a filled synthetic turf while eliminating the adverse effects of the use of sand.
It is another object of the present invention to extend the life of the resilient characteristics of a filled synthetic turf while still maintaining a high degree of directional stability for the synthetic backing.
It is still another object of the present invention to attain a long lasting, uniformly resilient athletic playing surface at a relatively low cost, and which is sufficiently versatile in design to accommodate a number of potential structural enhancements.
The present invention accomplishes these objects for a filled synthetic turf by using a particulate fill comprising at least some particles other than sand, i.e. particles such as gravel, to serve as a xe2x80x9cballastxe2x80x9d to hold down the backing. In one aspect of the present invention, the filled synthetic turf has a multi-layered particulate fill, the lower layer being a heavy particulate such as gravel, to serve as a xe2x80x9cballastxe2x80x9d to hold down the backing with an upper layer of resilient particles such as rubber over the ballast layer.
The filled synthetic turf comprises a backing residing on a foundation; a plurality of grass-like pile filaments secured to the backing and extending generally upwardly therefrom and a particulate fill material residing on the backing. The foundation may be crushed stone, dirt, asphalt, concrete, a pad or any other supporting surface. For drainage purposes, one or more drainage members may comprise part of the foundation.
The backing is preferably a flexible, water permeable material but may be made of any desired material. The backing may be a single layer of material or multiple layers of material joined together.
A plurality of grass-like pile filaments are secured to the backing and extend generally upwardly therefrom. The pile filaments preferably comprise synthetic ribbons of a selected length. They may be made of nylon, polyethylene or a polyethylene/polypropylene blend or any other material. They may be tufted, adhesively or otherwise joined to the backing. The pile filaments are preferably dyed or colored green so as to resemble the appearance of natural grass.
The fill material resides upon the backing and extends upwardly to a desired height which is below the tops of the pile filaments. This gives the field a green appearance, resembling natural grass. In addition, the particulate fill prevents the pile filaments from moving or becoming trampled down.
In one aspect of the present invention, the particulate fill material is divided into at least two layers: a first lower layer of ballast particles located on top of the backing and a second upper layer of resilient particles residing above the first lower layer. The first lower layer is comprised of particles such as gravel which provide weight for holding the backing in place. According to the United States Golf Association (U.S.G.A.), gravel is defined as particles having a diameter greater than 2 millimeters and sand is defined as particles having a diameter less than 2 millimeters. Fine gravel is defined by the U.S.G.A. as particles having a diameter between 2 and 3.4 millimeters. Although the U.S.G.A. uses diameter to measure particulate size, the particles of the present invention need not be symmetrical, i.e. have a diameter. They may be irregularly shaped. The ballast particles of the present invention are not intended to be limited to gravel. One type of ballast particle which is suitable for the present invention has the following analysis: 100 percent passing through a 0.5 inch or 12 millimeter sieve; not more than 10 percent passing through a number 10 or 2 millimeter sieve; and not more than 5 percent passing through a number 18 or 1 millimeter sieve.
The second upper layer provides resiliency for the synthetic turf. The resilient particles are preferably synthetic particles such as rubber particles, commonly referred to as crumb rubber.
In one aspect of the present invention, the height of the first lower layer is approximately equal to the height of the second upper layer. However, the first lower layer and the second upper layer may be any desired height.
In another aspect of the present invention, the particulate fill material is a mixture of ballast particles and resilient particles mixed together.
In another aspect of the present invention, the filled synthetic turf is multi-layered comprising at least two layers of filled synthetic turf. A surface layer of filled synthetic turf like the one described hereinabove, resides above a subsurface comprising another filled synthetic turf. The subsurface comprises a subsurface backing with a plurality of subsurface pile filaments extending upwardly therefrom to a desired height. A subsurface fill material resides on the subsurface backing to a desired vertical height relative to the desired height of the subsurface pile filaments. The subsurface fill material includes at least some resilient particles. In one aspect of the present invention the subsurface fill material may comprise gravel or sand as a lower layer and resilient particles such as rubber particles as an upper layer. The subsurface fill material may be held in place with a polymeric coating applied to the subsurface fill material and the subsurface pile filaments. Other binders such as latex or urethane may be used to hold the subsurface fill material in place.
In yet another aspect of the present invention, the composition of the subsurface fill material and the desired height of the subsurface pile filaments may be selected to achieve a desired degree of shock absorption for the subsurface and for the synthetic turf located thereabove.
In yet another aspect of the present invention tubing may reside in the subsurface fill material above the subsurface backing and below the tops of the subsurface pile filaments. The tubing is adapted to be operatively connected to a pump or other device to convey fluid within the tubing to selectively heat or cool the subsurface and thereby heat or cool the filled synthetic turf located above the subsurface.